Self-stressed concrete pipe and method of manufacture



Sept, 16, 1969 E. K. RICE ET AL 3,467,144

SELF-STRESSED CONCRETE PIPE AND METHOD OF' MANUFACTURE INVENTORS EDWARD K R/CE l/1//././ ME CU E70/v Arroz/V545 Sept. 16, 1969 E. K. RICE ET AL 3,467,144

SELF-STRESSED CONCRETE PIPE AND METHOD OF MANUFACTURE Filed May e, 1965 2 Sheets-Sheet 2 I H a INVENTOR pli-@ EDWARD K. Q/CE WM A/145.60 570/1/ 3% ATTO MEMS United States Patent C) 3,467,144 SELF-STRESSED CONCRETE PIPE AND METHOD F MANUFACTURE Edward K. Rice, Los Angeles, Calif., and William E. Cureton, Waco, Tex., assignors, by mesne assignments, to Stressed Pipe Research Ltd., a limited partnership of Texas Filed May 6, 1965, Ser. No. 453,705 Int. Cl. F161 9/08; B281) 21 60 U.S. Cl. 138-176 4 Claims ABSTRACT 0F THE DISCLOSURE This invention relates to self-stressed concrete pipe and method of manufacture, and included in the objects of this invention are:

First, to provide a self-stressed reinforced concrete pipe and method of manufacture which utilizes concrete cement compounded so as to expand as it sets to the extent that reinforcing therein is placed under tension, such as the concrete made from cement disclosed in Patent No. 3,155,526, issued Nov. 3, 1964.

Second, to provide a self-stressed reinforced concrete pipe and method of manufacture wherein the concrete throughout the pipe and especially at the ends thereof is placed under compression and constrained to produce a pipe capable of withstanding substantial internal pressures without subjecting the concrete to tensile loads.

Third, to provide a self-stressed reinforced concrete pipe which incorporates novelly arranged steel lined telescoping end portions which may be readily joined and sealed by an O-ring type sealing element.

Fourth, to provide a self-stressed reinforced concrete pipe and method of manufacture which may incorporate an impervious shell arranged under hoop tension by concrete cement expanded therein, and covered by other concrete cement, wire wrapped in such a manner as to be placed under compression.

Fifth, to provide a method of manufacturing reinforced concrete pipe which may utilize centrifugal casting techniques or end casting techniques, in conjunction with other manufacturing steps which effects tensioning of the reinforcing and compressing of the concrete.

With the above and other objects in view, as may appear hereinafter, reference is directed to the accompanying drawings in which:

FIGURE 1 is a fragmentary sectional view showing one wall of a pair of pipe sections joined together and illustrating one embodiment of the invention.

FIGURE f2 is a fragmentary sectional view showing the spigot end of the concrete pipe.

FIGURE 3 is a similar fragmentary sectional view showing the bell end of the concrete pipe.

FIGURE 4 is a fragmentary sectional view similar to FIGURE 1 showing a modified form of the concrete pipe.

FIGURE 5 is a fragmentary longitudinal sectional View of the form of pipe shown in FIGURES l through 3 encased in a mold suitable for a centrifugal casting operation.

FIGURE 6 is a fragmentary sectional view showing the reinforcing structure of a concrete pipe disposed in another type of form intended for introduction of the concrete longitudinally.

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FIGURE 7 is a fragmentary sectional view showing the reinforcing structure illustrated in FIGURE 4 constrained withn a form intended for centrifugal casting.

FIGURE 8 is a fragmentary transverse sectional view taken through 8 8 of FIGURE 7.

FIGURE 9 is a fragmentary sectional view illustrating a manner of applying an outer concrete sleeve and additional reinforcing to complete the type of pipe shown in FIGURE 4.

FIGURE 10 is a fragmentary sectional view of two adjacent ends of pipe sections illustrating a modified construction wherein each section is provided with the spigot ends and are joined by a collar.

Reference is first directed to FIGURES l through 3. The concrete pipe here illustrated includes a constraining end cap 1 which forms the spigot end of the pipe. rPhe end cap is formed of tension resisting metal of appropriate thickness to withstand the force imposed and includes a cylindrical portion Z joined at one end to a radially inwardly directed flange 3 which defines the extremity of the pipe section and in turn is provided with an annular reentrant lip 4.

The opposite end of the concrete pipe is also provided with a constraining end cap 5 which defines the spigot end of the pipe. The cap 5 includes a cylindrical portion 6 slightly larger in diameter than the cylindrical portion 2 at the end cap 1 so as to slip freely over as shown in FIGURE l. The cylindrical portion is joined to a radially inwardly directed flange 7 which, when two pipe sections are joined, confronts the flange 3 of the adjacent pipe section. The flange 7 terminates an axially directed annular lip 8. The opposite axial end of the cylindrical portion is provided with a radially outwardly directed flange 9 which forms the axial extremity of the bell end of the pipe and is provided with an annular axially directed lip 10.

The cylindrical portions 2 and 6 are provided with annular grooves 11 and 12 which register with each other when sections of the pipe are joined and receive an O ring 13.

The end caps 1 and 5 are connected by tension resisting axial reinforcing 14 welded to the cylindrical portions 2 and 6 respectively. The axial reinforcing 14 is covered by helical tension resisting reinforcing 15. The reinforcing 14 and 15 is formed of heavy gauge wire. In some instances, a wire mesh may be substituted for the reinforcing 14 and 15.

As will be explained in more detail hereinafter, a cylindrical concrete body 16 is provided between the end caps 1 and 5. The cylindrical portions 2 and 6 are so dimensioned that they are located near the outer periphery of the pipe. That is, the wall thickness from the cylindrical portions outwardly is substantially less than the wall thickness inwardly from the cylindrical portions, and the reinforcing is located in the radially outer portion of the concrete body.

It is preferred that the concrete extend radially outwardly beyond annular lip 10 and radially inward of the annular lips 4 and 8 and that these portions be beveled so that when two pipe sections are joined, the space therebetween may be filled with grouting 17 so as to seal the metal end caps 1 and 5.

It is essential that the concrete forming the body 16 be of the expansive type made from, for example, the type of cement disclosed in Patent No. 3,155,526 issued Nov. 3, 1964. During the curing of concrete pipe containing expansive cement, the reinforcing 14 and 15 is placed under tension. In other words, the reinforcing restricts the amount of expansion of the concrete so that, as a result, the concrete is placed under compression. Inasmuch as the prestressing is accomplished by chemical action, it is customary to refer to the resulting structure as being chemically prestressed.

Heretofore attempts to chemically prestress concrete pipe have resulted in a failure to obtain uniform prestressing throughout the length of the pipe and especially at the ends thereof. It is in this regard that the end caps 1 and 5 are of particular importance. The end caps being connected by the axial reinforcing 14 insure that the concrete throughout the entire length of the pipe is prestressed axially and the spigot end in particular is prestressed radially by reason of the cylindrical portion 2. It will be observed that by reason of the fact that the reinforcing is relatively close to the outside surface of the pipe, the major portions of the walls are under compression. This does not mean that the concrete immediately beyond the reinforcing is free of constraint. On the contrary, by reason of the bond established between the particles of the concrete and with the reinforcing, a major portion of the concrete beyond the reinforcing is subject to compressive loads.

Reference is now directed to FIGURE 4. This construction utilizes the end caps 1 and 5. In place of the reinforcing 14 and 15 the end caps are joined by tubular reinforcing 18 in the form of a metal sleeve. The sleeve may be continuous and without perforations so as to form an impermeable membrane; however, the sleeve may be perforated if desired. The sleeve may constitute, with the end caps, the sole reinforcing and is placed under tension by the expansive force of the concrete of an internal concrete body 19 of expansive concrete.

The outer surface of the sleeve may be covered with conventional concrete or other protective coating; however, it is preferred to apply an outer shell 21 of expansive concrete containing helical reinforcing 22.

Several methods may be employed in the manufacture of concrete pipe. For example, as shown in FIGURE 5, the concrete pipe with its reinforcing structure comprising the end caps 1 and 5 and the reinforcing 14 and 15, or the tubular reinforcing 18 if it is perforated, may be centrifugally cast. To accomplish this, end rings 23 and 24 are provided which receive the end caps 1 and 5 respectively and are shaped to conform thereto. The end rings are joined by a casting shell 2S. The form provided by the casting shell and end rings is arranged to be rotated in the conventional manner. During rotation, expansive concrete is introduced until the space between the end rings 23 and 24 is filled. After the concrete has undergone initial set, the casting shell and end rings are removed so that the concrete may expand and place the reinforcing under tension. Some expansive force may be exerted during the setting period; however, sutlicient additional expansion occurs during the curing period to insure that the reinforcing is placed under proper tension.

Reference is now directed to FIGURE 6, which il1ustrates a means whereby the concrete pipe may be formed in a stationary mold. In this case, the stationary mold includes a bottom plate 26, a cylindrical inner form or shell 27 and a cylindrical outer form or shell 28. The spigot forming end cap 1 may be positioned at the bottom of the mold and the bell forming end cap may be located at the top end of the mold and held in place by an end cap retainer rib 29 forming a part of the outer shell.

In this case, the end cap 5 is provided with perforations 30 and 31 formed in the flanges 7 and 9 respectively.l The outer form may continue above the reinforcing structure to form a funnel 32 to aid in the pouring of concrete into the form and around the reinforcing structure. The form may be vibrated in a conventional manner to insure packing of the concrete. In this case also, the concrete is allowed to set and at least the outer form is removed to allow the concrete to expand to the extent permitted by the reinforcing structure.

Reference is now directed to FIGURE 7 which illustrates a means of manufacturing the type of pipe shown in FIGURE 4. In `this case, the tubular reinforcing 18 and the end caps 1 and 5 are placed between end rings 33 and 34. In this case, it is desirable to place the tubular reinforcing 18 as well as the cylindrical portions of the end caps under radial compression. This may be accomplished in several ways, for instance, by an outer compression form 35 comprising several segments 36 joined by bolts 37. While the reinforcing structure is so constrained, the internal concrete body 19 is introduced, for example by a conventional centrifugal casting process; however, it should be noted that if desired, the type of internal form shown in FIGURE 6 may be employed so that the concrete may be introduced endwise.

As in the previous methods, the expansive concrete is permitted to undergo an intial set, then the form is removed. The tubular reinforcing 18 is then covered with the outer concrete layer or shell 21. For example, in the manner shown in FIGURE 9 in which the concrete is forced into the -pipe by conventional concrete guns and at the same time, the reinforcing 22 is wrapped thereon.

Reference is now directed to FIGURE 10. In the previous constructions, the concrete pipe has been illustrated as having a spigot end and a bell end. In some cases, however, it is desirable to provide two spigot ends as shown in FIGURE 10 in which cases, the pipe sections are joined by a collar 38'which is provided with an internal metal lining 39 having flanged ends 40 to receive a concrete sleeve 41 and reinforcing 42. If desired, the concrete sleeve may be formed of expansive concrete.

While particular embodiments of this invention have been shown and described, it is not intended to limit the same to the details of the construction set forth, but instead, the convention embraces such changes, modifications and equivalents of the various parts and their relationships as come within the purview of the appended claims.

We claim:

1. A selfstressed concrete pipe, comprising:

(a) a tubular concrete body formed of concrete which expands during its curing cycle;

(b) expansion resisting constraining caps at the ends of said concrete body;

(c) axially extending reinforcing within said concrete body and secured to said end caps, said reinforcing being tension resisting and being bonded to said concrete to limit axial expansion of said concrete body thereby to place said concrete body under axial compression;

(d) and circular reinforcing within said concrete body, said circular reinforcing being tension resisting and being bonded to said concrete to limit radial expansion of said concrete body thereby to place said concrete body under circumferential compression throughout its wall thickness;

(e) said constraining caps being formed of tension mesisting material and at least one of said caps including an internal flange overlying an end of said concrete body and an exposed cylindrical portion resisting radial expansion of the end portion of said concrete body.

2. A self-stressed reinforced concrete pipe as set forth in claim 1, wherein:

(a) said axial reinforcing is a cylindrical cage of metal rods.

3. A self-stressed reinforced concrete pipe as set forth in claim 1, wherein:

(a) said axial and circumferential reinforcing is a metal tube.

4. A self-stressed reinforced concrete pipe as set forth in claim 1, wherein:

(a) the other of said constraining caps including an exposed internal flange set within `the opposite end of said concrete body, and an internally exposed cylindrical portion continuing therefrom to the end of said concrete body;

(b) said constraining caps being dimensioned for telescoping engagement thereby to connect a series of concrete bodies end-to-end.

References Cited UNITED STATES PATENTS 2,709,845 6/1955 Serkin 13S-174 XR 3,290,840 12/ 1966 Middendorf 52-223 2,348,477

6 2,569,612 10/1951 Laurent 138-176 X 2,698,193 12/1954 Kennis-on 138-176 X OTHER REFERENCES Chemical Prestressing of Concrete Elements Using EX- panding Cements by T. Y. Lin and A. Klein, American Concrete Institute, Proceedings, volume 60, Number 9, September 1963, pp. 1187-1218.

5/ 1944 Jenkins 13S-176 X 10 LAVERNE D. GEIGER. Primary Examiner 

